1. Field of the Invention
The present invention generally relates to a radio frequency (RF) module, and more particularly to a dual-band multi-mode RF module.
2. Description of the Related Art
There has been explosive adoption of wireless LAN technology in the corporate environment and hot-spot areas since the finalization of IEEE 802.11a/b/g and Hiperlan-2 standards. The widely-deployed 802.11b network, operating in the 2.4-GHz Industrial-Scientific-Medical band with 83 MHz bandwidth, provides a maximum data rate of 11 Mbps, whereas the 802.11a and Hiperlan-2 standards, operating in the 5-GHz band with 300 MHz bandwidth, can support up to 54 Mbps data rate by utilizing the orthogonal frequency division multiplexing technique.
The effective coverage area of a single 2.4-GHz 802.11b/g access point is likely greater than that of a 5.2-GHz 802.11a. However, a greater number of users must share the limited 83 MHz spectrum. The data throughput is reduced when many users simultaneously access the 2.4-GHz WLAN network. A straight-forward solution by adding more access points does not necessarily improve throughput because the in-band interference problem emerges as a result of the limited spectrum (83 MHz) shared by multiple access points. In contrast, the 802.11a network experiences less interference problem for multiple access-point deployment because of its smaller coverage area and greater bandwidth allocation (300 MHz bandwidth). From the other aspect of product adoption rate, the 802.11b network has been deployed worldwide so that it is important to maintain the high-data-rate WLAN network backward compatible with the existing 802.11b products. Hence, the 2.4-GHz 802.11b/g and 5.2-GHz 802.11a/Hiperlan-2 networks are complementary and will coexist in the coming years.
The rapid development of the coexistence operation of multi-mode wireless LAN has been driving conventional RF and base-band transceivers to have integrated multi-band and multi-functional characteristics. Conventional dual-band WLAN Transceivers adopt the parallel transceiver topology. Namely, two independent RF modules of 2.4 GHz and 5.2 GHz are combined in parallel with extra band-selection switches, used for switching the 2.4-GHz and 5.2-GHz RF. However, this parallel topology causes larger circuit size, more power dissipation, more component count, and higher cost. Numbers of work have been demonstrated the different integration effort on multi-band, multimode receivers. On the 2.4/5.2 GHz wireless LANs, the concept of concurrent dual-band receiver was proposed by Hashemi and Hajimiri, entitled “Concurrent Multi-band Low-Noise Amplifiers-Theory, Design, and Applications,” IEEE Transactions Microwave Theory and Techniques, vol. 50, no. 1, pp. 288-301, January 2002,which provides a concurrent amplifier of 2.4 GHz and 5.2 GHz and a dual-band receiving topology. A concurrent dual-band CMOS LNA was analyzed and designed to verify the concurrent circuit concept. Above work is focused on the dual-band integration of the receiver only. No prior art works on the dual-band transmitter.
According to the above problems, there is a need to provide a dual-band transmitting/receiving topology for the 2.4/5.2 GHz WLAN. The modules of the present dual-band RF circuit determine the device characteristics of each dual-band circuit according to the system power, gain and noise. Two independent RF modules of 2.4 GHz and 5.2 GHz are effectively combined together, therefore the circuit size, power dissipation, component count, and cost can be dramatically reduced.